In a phone terminal having a phone book connected to a general public line, there have conventionally been proposed methods of notifying changed contents of one's own phone number through an electronic mail message to a partner so as to execute phone book data updating work, and analyzing the contents of the mail message on partner's phone terminal side to automatically update the phone book data (Japanese Patent Application Laid-open No. 2003-108481 and Japanese Patent Application Laid-open No. 2003-108482).
Recently, there is known a technology of carrying out voice (or even image) communication not only by a phone terminal connected to the general public line but also by an Internet phone (VoIP) system has been known. It is believed that the automatic updating of the phone book data through an electronic mail message as described above can be also carried out by an IP phone terminal connected to an IP network.